The present invention relates in general to unreeling, and more particularly to a system for controlling the deployment of a radiosonde relative to a balloon from which it is suspended.
Meteorological balloons, usually of high quality natural rubber latex, chloroprene, or Mylar, are used to lift radiosondes to high altitudes for automatic upper air measurements. While ascending, measurements of temperature, humidity and barometric pressure can be transmitted on an RF carrier to a remote station for recording and processing. Radar and radiotheodolites may track the flight to provide data for computing wind speed and direction.
Some radiosondes utilize highly accurate navigation (NAVAID) systems such as the world-wide Loran-C, international Omega, or VLF transmissions for tracking and wind data. Signals transmitted by these systems are at very low frequencies (10-100 kHz) and for best reception require long receiving antennas, for example over 15 feet. Customarily, the antenna includes a metal wire that is stored in the radiosonde for shipment. The wire is withdrawn from the radiosonde and wrapped helically about the cord used to connect the radiosonde to the balloon.
In high winds or onboard ship, two or more operators are frequently required to safely launch the balloon radiosonde without tangling the connecting cord. To minimize the risk of entanglement, the cord is stored on a single reel from which it is paid out as the balloon and radiosonde ascend. The pay out rate is regulated to avoid excessive unwinding. Prior art pay out devices, or so-called dereelers, generally have been complex and costly to manufacture. Their added weight also requires larger balloons with proportionately more gas for adequate lifting. In one system, the cord is paid out from a dereeler, separately housed between the balloon and the radiosonde, at a rate controlled by a ratchet and escapement mechanism. In addition to its complexity and high cost, the inertia of the reel coupled with its intermittent rotation produces sudden and repetitive tension on the cord requiring heavier weight cord and to ensure against breakage. In another deployment system of equal complexity, disclosed in U.S. Pat. No. 1,307,155 to Adolf W. Schramm, an antenna pays out from a reel within an airborne vehicle at a rate controlled by weights rotating with the reel and centrifugally acting on the inner surface of a brake drum.
While reliability is a major factor in the design of radiosondes, costs are a critical factor in the production of balloon radiosondes because they are not normally recovered after ascent. For this reason, simplicity, ease of assembly, and low cost materials of construction are important considerations for the design of an antenna deployment system for expendable radiosondes.